Unnatural Selection

Trophy hunting and commercial fishing are driving the most rapid evolutionary changes ever observed in the wild, according to a study published this week in the online issue of the Proceedings of the National Academy of Sciences. The study was co-authored by UVic biologist Dr. Tom Reimchen and led by Dr. Chris Darimont, who began the work while a biology PhD candidate at UVic. He’s now a postdoctoral researcher at the University of California at Santa Cruz.
        Based on an extensive literature review that tracked 29 species in 40 geographic systems around the world, the study concludes that human predation is accelerating the rate of trait changes in prey animals by 300 per cent above the pace within natural systems. Body sizes of harvested animals—such as bighorn sheep, caribou, salmon and cod—have shrunk by 20 per cent from previous generations, while shifts to breeding at smaller sizes and younger ages have averaged 25 per cent. This spells trouble, say the researchers, because early breeders generally produce fewer offspring, further reducing the ability of populations to recover from large harvests.
        “Most predators target young animals and avoid reproductive adults, but as super-predators, humans do the opposite,” says Reimchen. “This has huge implications for the long-term viability of some animal populations and ecosystems and, ultimately, for the commercial harvesting industries that depend on them.”
        The authors argue that the only way to avoid losing the traits we value and depend on in wild prey is to mimic natural predators, which means greatly reducing the number of animals we kill and foregoing our desire for the largest.

 

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